Re: [PATCH 1/2] mm: shmem: avoid allocating huge pages larger than MAX_PAGECACHE_ORDER for shmem

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2024/7/31 16:56, Baolin Wang wrote:
> 
> 
> On 2024/7/31 14:18, Barry Song wrote:
>> On Wed, Jul 31, 2024 at 1:46 PM Baolin Wang
>> <baolin.wang@linux.alibaba.com> wrote:
>>>
>>> Similar to commit d659b715e94ac ("mm/huge_memory: avoid PMD-size page 
>>> cache
>>> if needed"), ARM64 can support 512MB PMD-sized THP when the base page 
>>> size is
>>> 64KB, which is larger than the maximum supported page cache size 
>>> MAX_PAGECACHE_ORDER.
>>> This is not expected. To fix this issue, use 
>>> THP_ORDERS_ALL_FILE_DEFAULT for
>>> shmem to filter allowable huge orders.
>>>
>>> Fixes: e7a2ab7b3bb5 ("mm: shmem: add mTHP support for anonymous shmem")
>>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>>
>> Reviewed-by: Barry Song <baohua@kernel.org>
> 
> Thanks for reviewing.
> 
>>
>>> ---
>>>   mm/shmem.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/mm/shmem.c b/mm/shmem.c
>>> index 2faa9daaf54b..a4332a97558c 100644
>>> --- a/mm/shmem.c
>>> +++ b/mm/shmem.c
>>> @@ -1630,10 +1630,10 @@ unsigned long 
>>> shmem_allowable_huge_orders(struct inode *inode,
>>>          unsigned long within_size_orders = 
>>> READ_ONCE(huge_shmem_orders_within_size);
>>>          unsigned long vm_flags = vma->vm_flags;
>>>          /*
>>> -        * Check all the (large) orders below HPAGE_PMD_ORDER + 1 that
>>> +        * Check all the (large) orders below MAX_PAGECACHE_ORDER + 1 
>>> that
>>>           * are enabled for this vma.
>>
>> Nit:
>> THP_ORDERS_ALL_FILE_DEFAULT should be self-explanatory enough.
>> I feel we don't need this comment?
> 
> Sure.
> 
> Andrew, please help to squash the following changes into this patch. 
> Thanks.

Maybe drop unsigned long orders too?

diff --git a/mm/shmem.c b/mm/shmem.c
index 6af95f595d6f..8485eb6f2ec4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1638,11 +1638,6 @@ unsigned long shmem_allowable_huge_orders(struct 
inode *inode,
         unsigned long mask = READ_ONCE(huge_shmem_orders_always);
         unsigned long within_size_orders = 
READ_ONCE(huge_shmem_orders_within_size);
         unsigned long vm_flags = vma ? vma->vm_flags : 0;
-       /*
-        * Check all the (large) orders below HPAGE_PMD_ORDER + 1 that
-        * are enabled for this vma.
-        */
-       unsigned long orders = BIT(PMD_ORDER + 1) - 1;
         bool global_huge;
         loff_t i_size;
         int order;
@@ -1698,7 +1693,7 @@ unsigned long shmem_allowable_huge_orders(struct 
inode *inode,
         if (global_huge)
                 mask |= READ_ONCE(huge_shmem_orders_inherit);

-       return orders & mask;
+       return THP_ORDERS_ALL_FILE_DEFAULT & mask;
  }

> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 6e9836b1bd1d..432faec21547 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1629,10 +1629,6 @@ unsigned long shmem_allowable_huge_orders(struct 
> inode *inode,
>          unsigned long mask = READ_ONCE(huge_shmem_orders_always);
>          unsigned long within_size_orders = 
> READ_ONCE(huge_shmem_orders_within_size);
>          unsigned long vm_flags = vma->vm_flags;
> -       /*
> -        * Check all the (large) orders below MAX_PAGECACHE_ORDER + 1 that
> -        * are enabled for this vma.
> -        */
>          unsigned long orders = THP_ORDERS_ALL_FILE_DEFAULT;
>          loff_t i_size;
>          int order;
>